Method of Controlling the Temperature of Oil for Vehicle Powertrain

ABSTRACT

A thermal management unit for a vehicle powertrain includes an integrated oil heater, a control valve, and a pressure relief valve. A remote oil cooler is connected to fluid ports of the thermal management unit. Transmission oil is received into the thermal management unit and is directed to one or both of the transmission oil heater and the transmission oil cooler. A portion of the flow of oil can be internally bypassed through the pressure relief valve to maintain the pressure of the oil below a threshold. The flow of oil is directed through the control valve after having been heated and/or cooled, and the proportions of oil being directed through the oil heater and the oil cooler are determined by the temperature of the oil in the control valve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of U.S. patent application Ser. No. 14/605,294, which was filed on Jan. 26,2015, the entire contents of which are hereby incorporated by reference.

BACKGROUND

The invention relates to integrated heat exchanger and valve assemblies, and particularly relates to heat exchanger and valve assemblies for regulating the temperature of fluid for a vehicle powertrain.

Heat exchange systems to regulate the temperature of fluids to be above a minimum threshold, below a maximum threshold, or within a desirable range bounded by a minimum and a maximum threshold are known. Such heat exchange systems typically include one or more heat exchangers and one or more flow control devices to control the flow of fluid to the one or more heat exchangers. Vehicle powertrains in particular require such heat exchange systems in order to properly regulate the temperature of working fluid such as coolant, engine oil, transmission oil, and the like.

With ever increasing incentives to improve overall fuel economy and system efficiency, properly regulating the temperature of fluids within a vehicle powertrain has become of greater importance. Such temperature regulation can require both a heat exchanger to rapidly heat the fluid during cold startup of the vehicle powertrain, and a heat exchanger to reject waste heat accumulated in the fluid during operation of the vehicle powertrain. Control devices (including valves and the like) can be used to selectively route the fluid to the heat exchangers in order to meet these objectives.

Advantages can be found in integrating portions of these heat exchange systems into a thermal management unit, thereby reducing the number of interconnections and simplifying installation of the heat exchange system into the vehicle powertrain.

SUMMARY

According to an embodiment of the invention, a thermal management unit for a vehicle powertrain includes a valve operable to selectively route fluid between a valve outlet and first and second valve inlets, a first fluid port to receive a flow of oil from the vehicle powertrain, a second fluid port to deliver a flow of oil to the vehicle powertrain, a third fluid port fluidly connected to the first fluid port by way of a first flow path extending through the thermal management unit, and a fourth fluid port fluidly connected to one of the first and second valve inlets by way of a second flow path extending through the thermal management unit. The thermal management unit further includes an integrated transmission oil heater having a fluid inlet manifold, a fluid outlet manifold, and a plurality of flow structures extending between the fluid inlet manifold and the fluid outlet manifold. The fluid inlet manifold is fluidly connected to the first fluid port by way of a third flow path extending through the thermal management unit and the fluid outlet manifold is fluidly connected to the other of the first and second valve inlets by way of a fourth flow path extending through the thermal management unit. A fifth flow path extends between and fluidly connects the second fluid port and valve outlet. A shunt flow path extends from the first fluid port and fluidly connects to one of the second flow path, the fourth flow path, and the fifth flow path at an end of the shunt flow path. A pressure relief valve is arranged along the shunt flow path to block the flow of oil along the shunt flow path when the pressure differential between the first fluid port and the end of the shunt flow path is below a threshold, and to allow flow of oil along the shunt flow path when the pressure differential exceeds that threshold.

In some embodiments, the valve includes a sensing element configured to operate the valve in response to the temperature of oil passing over the sensing element, and in some particular embodiments the sensing element is a wax motor. In some embodiments the entire flow of oil entering through the first fluid port is directed over the sensing element.

In some embodiments, the thermal management unit includes a cast structure having a central bore extending linearly therethrough. Both the valve and the pressure relief valve are arranged within the central bore.

In some embodiments, the valve includes a movable shuttle having one or more window apertures arranged therein. In some such embodiments at least some of the one or more window apertures define the valve outlet. In some embodiments at least some of the window apertures define one of the first and second valve inlets, and movement of the movable shuttle operates to open and close that one of the first and second valve inlets.

According to another embodiment of the invention, a method of controlling the temperature of oil for a vehicle powertrain includes receiving a flow of oil from the vehicle powertrain into a thermal management unit at a first pressure, and directing at least some of the flow of oil through at least one of a transmission oil heater and a transmission oil cooler. That flow of oil is received into a valve arranged within the thermal management unit after passing through the at least one of a transmission oil heater and a transmission oil cooler, and any remaining flow of oil is directed through a bypass arranged within the thermal management unit to avoid it passing through either of the transmission oil heater and the transmission oil cooler. The temperature of oil received into the valve is measured, and the flow of oil is returned to the vehicle powertrain from the thermal management unit.

In some embodiments, the oil is received into the valve at a second pressure lower than the first pressure. In some such embodiments the amount of oil passing through the bypass is determined in response to a pressure differential between the first pressure and the second pressure. In some embodiments the step of measuring a temperature of oil includes directing the entire flow of oil received into the thermal management unit over a temperature-responsive element arranged within the valve.

According to another embodiment of the invention, a method of managing oil for a vehicle powertrain includes receiving a flow of oil from the vehicle powertrain into a thermal management unit at a first temperature below a threshold temperature and dividing the flow of oil into a first portion and a second portion. The first portion is directed into a transmission oil heater integrated into the thermal management unit, and is heated. The first portion is then recombined with the second portion, the second portion having bypassed the transmission oil heater, so that the recombined flow is at a second temperature higher than the first temperature. The recombined flow of oil is received into a valve located within the thermal management unit and is passed over a temperature-responsive element arranged within the valve, after which the recombined flow of oil is returned to the vehicle powertrain from the thermal management unit at the second temperature.

In some embodiments the flow of oil is a first flow of oil, and a second flow of oil is received from the vehicle powertrain into the thermal management unit some time after having returned the first flow of oil to the vehicle powertrain. Substantially all of the second flow of oil is directed into the transmission oil heater and is heated. The second flow of oil is received into the valve at a temperature substantially equal to the threshold temperature, and an actuator of the valve is actuated in response to passing the second flow of oil over the temperature-responsive element so that subsequent flows of oil into the thermal management unit are at least partially directed through an oil cooler associated with the vehicle powertrain.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a thermal management unit according to an embodiment of the invention.

FIG. 2 is a partially exploded perspective view of the thermal management unit of FIG. 1.

FIG. 3 is a perspective view of a heat exchanger that is part of the thermal management unit of FIG. 1.

FIG. 4 is an exploded perspective view of the heat exchanger of FIG. 3.

FIG. 5 is a top view of the thermal management unit of FIG. 1.

FIG. 6 is a sectional end view of the thermal management unit of FIG. 1, viewed along the lines VI-VI of FIG. 5.

FIG. 7 is a sectional side view of the thermal management unit of FIG. 1, viewed along the lines VII-VII of FIG. 5.

FIG. 8 is a sectional side view of the thermal management unit of FIG. 1, viewed along the lines VIII-VIII of FIG. 5.

FIG. 9 is a sectional bottom view of the thermal management unit of FIG. 1, viewed along the lines IX-IX of FIG. 8.

FIGS. 10A and 10B are perspective views of a control valve of the thermal management unit of FIG.1, shown in two different operating states.

FIGS. 11A and 11B are sectional side views of the installed control valve of FIGS. 10A and 10B in the two different operating states.

FIG. 12 is a cut-away perspective view of a pressure relief valve of the thermal management unit of FIG.1.

FIG. 13 is a diagrammatic view of a thermal management unit coupled to a vehicle powertrain according to an embodiment of the invention.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.

A thermal management unit 1 according to an embodiment of the invention is shown in FIG. 1 and is especially well suited for use with the powertrain of a vehicle such as an automobile, truck, bus, agricultural or construction equipment, etc. The vehicle powertrain, as referred to in this context, includes those vehicle sub-systems responsible for producing motion of the vehicle, and includes (without limitation) the engine, transmission, brakes, and power steering. The thermal management unit 1 can be employed to maintain the operating temperature of a working fluid of the vehicle powertrain within an acceptable range. A particular working fluid for which the thermal management unit 1 is especially well suited is the oil commonly referred to as automatic transmission fluid, which is used within the vehicle powertrain as both a lubricant and a hydraulic fluid. This oil has been developed with specific properties (e.g. viscosity, lubricity, temperature capability) in order to both withstand the harsh operating environments of vehicle powertrains, and to optimize the performance of the powertrain. Some of these properties vary considerably with temperature, and it can therefore be especially important for the operating temperature of the oil to be maintained within a fairly narrow range for optimum performance and lifetime.

The diagram of FIG. 13 illustrates an exemplary manner by which the thermal management unit 1 can be fluidly coupled to a vehicle powertrain 2. Oil from the vehicle powertrain is routed to and from the thermal management unit 1 by way of fluid lines 73, a first of which connects to an inlet port 11 of the thermal management unit 1, and a second of which connects to an outlet port 12 of the thermal management unit 1. Oil that is received into the thermal management unit 1 by way of the inlet port 11 can be selectively routed to a transmission oil heater 3 integrated with the thermal management unit 1, and/or to a transmission oil cooler 4 that can be located remotely from the thermal management unit 1. Alternatively, or in addition, at least some of the oil received through the inlet port 11 can be bypass both the transmission oil heater 3 and the transmission oil cooler 4 by passing through a pressure relief valve 6 arranged within the thermal management unit 1. A control valve 5 is additionally arranged within the thermal management unit 1 and receives the oil from each of the three possible flow paths in order to deliver the oil to the outlet port 12. The control valve 5 operates to selectively determine the proportions of oil flow through the transmission oil cooler 4 and the transmission oil heater 3, as will be described in further detail with respect to the specific embodiment of FIG. 1.

The transmission oil cooler 4 is a heat exchanger that is configured to reject heat from the oil in order to maintain the operating temperature of the oil below an upper threshold temperature. Such a heat exchanger is typically configured as an air-cooled heat exchanger that forms part of a vehicle cooling module, although other heat exchanger arrangements could alternatively be used depending upon the specifics of the vehicle application. Fluid lines 72 provide for coupling between the transmission oil cooler 4 and ports 13 and 14 of the thermal management unit 1 in order to enable the flow of oil to and from the transmission oil cooler 4.

The transmission oil heater 3 is a heat exchanger that is configured to provide heat to the oil in order to maintain the operating temperature of the oil above a lower threshold temperature. Such a heat exchanger is especially beneficial during startup of the vehicle powertrain, when the oil is likely to be cold. The viscosity of the oil is typically optimized for performance at the elevated operating temperature of the vehicle powertrain, and at lower temperatures the oil typically has a substantially higher viscosity. When the vehicle has been in a non-operating condition for hours in a low-temperature ambient environment the oil is likely to have cooled to a temperature at which the viscosity is many times greater than that optimized viscosity. In order to maintain proper operation of the vehicle powertrain, it is important for the oil to be circulating therethrough even when the oil is not yet up to its proper operating temperature. The circulation of the oil is typically accomplished by an oil pump forming part of the vehicle powertrain 2.

Circulation of the highly viscous cold oil requires substantially greater work input than circulation of the oil at proper operating temperature, resulting in substantial fuel economy reduction over that time period when the oil is not yet within its desired temperature range. Owing at least in part to the high thermal mass of the vehicle powertrain 2, it is not uncommon for the oil to have not yet reached that desirable operating temperature by the time the vehicle has reached its destination and is stopped, at which point the vehicle might remain in a non-operating condition for sufficient time to return the vehicle powertrain 2, and the oil, to the initial low temperatures so that the entire cycle repeats itself. As a consequence, the overall fuel economy of the vehicle can be severely compromised.

This situation can be remedied by facilitating the rapid warm-up of the oil through the use of the transmission oil heater 3. Coolant that is rapidly heated within the vehicle powertrain 2 (by, for example, being circulated directly over the cylinder heads of the engine of the vehicle powertrain 2) is routed to and from the transmission oil heater 3 by way of coolant lines 71 extending between the vehicle powertrain 2 and the thermal management unit 1. The coolant and the oil are both circulated through the transmission oil heater 3 in order to effect the rapid and efficient transfer of heat to the oil, thereby facilitating a more rapid warming of the oil to the desired operating temperature range.

The embodiment of FIG. 1 will now be described in further detail, with additional reference to the FIGS. 2-12. The thermal management unit 1 includes a cast housing 7 that is joined to a layered core heat exchanger 3 functioning as a transmission oil heater. Fluid ports 11 and 12 are provided within the cast housing 7 to provide for fluid couplings to respectively receive oil from, and return oil to, a vehicle powertrain. In addition, ports 13 and 14 are provided within the cast housing 7 to allow for fluid connections to a remotely located transmission oil cooler.

The transmission oil heater 3 of the exemplary embodiment is of a construction style wherein nested shells are arranged into a stack 21 which is joined to a base plate 22. An inlet port 23 and an outlet port 24 extend from the base plate 22 and sealingly engage (through the use of o-ring type seals 32) with apertures 47 and 48, respectively. The apertures 47 and 48 are provided within a mounting surface 46 of the cast housing 7, and the base plate 22 is secured to the mounting surface 46 through threaded fasteners 8, which extend through mounting holes 33 provided within the base plate 22 and engage corresponding threaded holes 41 of the cast housing 7. Alternatively, such securing of the transmission oil heater 3 to the housing 7 can be accomplished by other means such as spring clips, welding, etc.

As best seen in the exploded view of FIG. 4, the stack 21 includes alternating dimpled shells 27 and un-dimpled shells 28 with corresponding upturned peripheral flanges to allow the shells to nest together while providing space for fluid flow between the flat surfaces of adjacent shells. Manifolds 30 extend through the shells at two of the corners of the stack 21 at opposing short ends of the shells, with one of the manifolds 30 acting as an inlet manifold for the coolant and the other acting as an outlet manifold. The end of the stack 21 is closed off with a cap plate 31 that includes two coolant ports 36, each of which communicates with one of the coolant manifolds 30. Dimples of the dimpled shells 27 extend towards the flat surface of an adjacent un-dimpled shell 28, and the spaces between the dimples provide a coolant flow path between the coolant manifolds 30.

An oil inlet manifold 25 is provided at another of the corners of the shells, and an oil outlet manifold 26 is provided at the remaining corner. Flow plates 29 are received within the un-dimpled shells 28 and provide an oil flow path between the manifolds 25 and 26. The flow plates 29 can be, for example, lanced and offset fin plates that provide a tortuous flow path through the stack 21 in order to maximize the rate of heat transfer.

The base plate 22 is formed from three individual plates 22 a, 22 b, 22 c. A channel 35 is formed within the plates 22 b and 22 c to fluidly connect the outlet port 24 with the oil outlet manifold 26. Similarly, a channel 34 is formed within the plates 22 b and 22 c to fluidly connect the inlet port 23 with the oil inlet manifold 25. It should be understood, though, that in alternative embodiments the baseplate 22 can be constructed of a differing number of plates, and that in some embodiments the baseplate 22 can consist of a single plate.

The components of the transmission oil heater 3 are, in some especially preferred embodiments, aluminum alloy components, with at least some of the components having been clad with a braze alloy so that the transmission oil heater 3 can be entirely or substantially formed by brazing together the components.

During operation, a flow of coolant that has been heated by the vehicle powertrain 2 is circulated through a coolant line 71 to one of the ports 36 provided on the transmission oil heater 3, and is subsequently received into the coolant manifold 30 that is in direct fluid communication with that one of the ports 36. The coolant flow paths formed between the dimpled surfaces of the dimpled shells 27 and the facing surfaces of the un-dimpled shells 28 are in fluid communication with the coolant manifolds 30, so that the flow of coolant received into the transmission oil heater 3 can be circuited through the heater along those multiple flow paths. Simultaneously, a flow of transmission oil can be received into the transmission oil heater 3 by way of the port 23, and can be routed through the channel 34 towards the inlet manifold 25. Flow paths for the oil, formed by the flow plates 29, are in fluid communication with the inlet manifold 25 and the outlet manifold 26, and the oil received into the inlet manifold 25 is circulated through the transmission oil heater 3 along those flow paths. As the two fluid move through the transmission oil heater 3, heat from the coolant flow is transferred through the shells 27, 28 to the oil flow in order to heat the oil flow. The heated oil is collected in the outlet manifold 26, and is directed through the channel 35 in order to be removed from the transmission oil cooler 4 through the port 24. The cooled coolant is received into the other coolant manifold 30, and is removed through the other coolant port 36 to be returned back to the vehicle powertrain 2 along another coolant line 71.

It should be understood by those having skill in the art that the transmission oil heater 3 shown in the figures and described herein is but one exemplary heat exchanger that is especially well-suited for the purpose described. Details of the heat exchanger construction can vary from those described, and the details of the heat exchanger construction are not intended as a limitation upon the present invention.

As the flow of oil is received into the thermal management unit 1 through the port 11, internal flow channels within the housing 7 allow for the flow to be directed to multiple locations. As best seen in FIG. 7, a flow path 17 fluidly connects the port 11 with the inlet port 23 of the transmission oil heater 3, so that at least some of the flow of oil can be directed into the transmission oil heater 3. Another flow path 15 fluidly connects to the port 13, which can be used as a connection port for a fluid line 72 that connects the thermal management unit 1 to a remote transmission oil cooler 4. In this way, the flow of oil received into the thermal management unit 1 can be routed towards either the transmission oil cooler 4, the transmission oil heater 3, or both.

The inlet port 11 is arranged at one end of a central bore 42 that extends through the housing 7. Arranged within the central bore 42 are a pressure relief valve 6 and a control valve 5. Stepped diameter changes of the central bore 42 allow for the pressure relief valve 6 and the control valve 5 to be properly situated and retained within the housing 7. The pressure relief valve 6 is inserted from the end of the central bore 42 corresponding with the location of the inlet port 11, while the control valve 5 is inserted from the opposing end. A snap ring 53 is inserted into a snap ring groove 43 in order to secure the control valve 5 within the central bore 42.

The control valve 5 includes a movable shuttle 54 that travels along a longitudinal axis of the control valve 5 between a first operational state position depicted in FIG. 10A and FIG. 11A, and a second operational state position depicted in FIG. 10B and FIG. 11B. A sensing element 57 is centrally located within the movable shuttle 54, and contains an actuator 58 that is responsive to the temperature measured by the sensing element 57. In the exemplary embodiment the sensing element 57 is a wax motor, and contains a quantity of wax that is specifically formulated to undergo a phase change at a predefined threshold temperature. The phase change results in an increase of volume of the wax, which causes the actuator 58 to extend and displace the movable shuttle 54. A coil spring 59 is located between the movable shuttle 54 and a shoulder 44 of the central bore 42, so that the movement of the shuttle 54 caused by the extension of the actuator 58 compresses the spring 59. The spring 59 provides a restoring force to return the movable shuttle 54 back to its first operational state position when the actuator 58 retracts in response to a reduction of temperature sufficient to reverse the phase change of the wax motor.

The movable shuttle 54 is provided with circumferentially arranged window apertures 55. The exemplary embodiment shows multiple such window apertures 55 arranged to extend along the entire circumferential periphery of the movable shuttle 54, although in some embodiments a single window aperture extending along a substantial majority of the circumference could be employed. At least some of the window apertures 55 are in alignment with a flow channel 19 provided in the housing 7 along the entire travel stroke of the movable shuttle 54. The flow channel 19, as best seen in FIG. 6 and FIG. 9, fluidly connects to the outlet port 12. The window apertures 55 thus serve as a valve outlet to allow oil that is received into the control valve 5 to exit the control valve 5, and subsequently to be returned back to the vehicle powertrain 2 along the fluid line 73 that is connected to the outlet port 12.

An additional flow channel 16 is provided within the housing 7, and is connected to the port 14 to receive a flow of oil along the fluid line 72 from the transmission oil cooler 4, as best seen in FIG. 6 and FIGS. 8-9. Oil received into the flow channel 16 can be directed into the interior of the movable shuttle 54 through at least some of the window apertures 55 when the movable shuttle is in the second operational state position of FIG. 11B, but such flow of oil is prevented when the movable shuttle 54 is in the first operational state position of FIG. 11A. The window apertures 55 thus also function as a valve inlet for the control valve 5, which can be opened and closed in response to the temperature of the oil passing over the sensing element 57.

An additional inlet to the control valve 5 is provided by the open end 66 of the movable shuttle 54. When the movable shuttle 54 is in the first operational state position of FIG. 11A, flow can be received into the open end 66 from a flow channel 18 provided within the housing 7. The flow channel 18 connects to the port 24 of the transmission oil heater 3, as best seen in FIG. 8, and receives oil that has passed through the heater 3. When the movable shuttle 54 transitions to the second operational state position of FIG. 11B, it blocks flow in the channel 18 from reaching the inlet 66.

A shunt flow path 20 is provided within the central bore 42 of the housing 7, and provides a means by which oil received into the thermal management unit 1 through the inlet port 11 can reach the control valve 5 without passing through either the transmission oil heater 3 or the transmission oil cooler 4. The pressure relief valve 6 is located along the shunt flow path 20, and operates to block the flow of oil through the shunt flow path 20 under most conditions. When oil is allowed to flow through the shunt flow path 20, however, then that oil is able to pass through the control valve 5 by way of the inlet 66 regardless of the position of the movable shuttle 54.

FIGS. 11A and 11B depict the flow of oil through the control valve 5 in the two different operating state of the valve. In FIG. 11A movable shuttle 54 is in its first operational state position, corresponding to the temperature of the oil passing over the sensing element 57 being below the minimum threshold. The flow of oil, depicted by the solid arrow, passes from the flow channel 18 into the control valve 5 through the inlet 66, and exits the control valve 5 through the window apertures 55 to the flow channel 19. If the pressure relief valve 6 allows for any flow of oil through the shunt flow path 20, that oil travels along the dashed line and also enters the control valve 5 through the inlet 66, mixing with the oil received from the transmission oil heater 3 within the shuttle 54 of the control valve 5.

When the control valve 5 is in the second operational state position, as shown in FIG. 11B, the actuator 58 is fully extended and the movable shuttle 54 has translated completely to its second operational state position, resulting in the end of the movable shuttle 54 butting up against the shoulder 45. In this position, the shuttle 54 blocks the flow of oil from the flow channel 18, but oil is now able to flow into the control valve 54 from the flow channel 16, as at least some of the area of the window apertures 55 are now aligned with the flow channel 16. Again, any flow of oil through the shunt flow path 20 is received into the control valve 5 through the open end 66 of the movable shuttle 54.

It is especially of note that, in either of the operational states, all of the oil (i.e. both oil that is routed through the heater 3 and/or the cooler 4, and oil that is bypassed through the shunt flow path 20) passes over the sensing element 57. This allows for precise control of the temperature of the oil that is delivered to the vehicle powertrain 2. When the control valve is in the first operational state corresponding to FIG. 11A and the oil is being heated within the oil heater 3, the temperature of the oil passing over the sensing element 57 can eventually reach the threshold temperature at which the actuator 58 begin to extend. This will cause the movable shuttle 54 to translate, and when sufficient movement is achieved the control valve 5 will receive some proportion of flow from the transmission oil cooler 3 through the flow channel 16. An intermediate steady-state condition can be achieved wherein the movable shuttle 54 is at an intermediate position between the extremes of FIG. 11A and FIG. 11B, so that a portion of the oil received into the valve 5 is routed through the oil heater 3 and another portion of the oil received into the valve 5 is routed through the oil cooler 4.

When the temperature of the oil passing over the sensing element reaches the upper threshold, the actuator 58 will have extended sufficiently to displace the movable shuttle 54 so as to engage the shoulder 45. As long as the flow of oil passing over the sensing element 57 is sufficiently warm to maintain the extension of the actuator 58, this position of the valve will ensure that oil is directed through the oil cooler 4 rather than through the oil heater 3. Damage to the control valve 5 caused by over-extension of the actuator 58 (as might result from oil temperatures sufficiently in excess of the upper threshold) can be avoided by the inclusion of an over-stroke prevention spring 60. The over-stroke prevention spring 60 has a higher spring constant than does the spring 59, so that compression of the over-stroke prevention spring 60 does not occur until the movable shuttle 54 engages the shoulder 45.

The pressure relief valve 6 of the exemplary embodiment is shown in greater detail in FIG. 12. The pressure relief valve 6 includes a cap 62 joined to a cylindrical sleeve 61, with the sleeve 61 having an outer diameter that is somewhat smaller than the diameter of the central bore 42 in the region of the shunt flow path 20. A biasing spring 64 and plunger 63 are arranged within the cylindrical sleeve 61. The biasing spring 64 is maintained in a partially compressed state so that the plunger 63 is forced into contact with a seating surface of the cap 62. The cap 62 can be press-fit into the central bore 42 so that flow through the shunt flow path 20 is prevented when the plunger 63 is disposed against the seating surface of the cap 62. The end of the sleeve 61 opposite the cap 62 is at least partially open so that the plunger 63 is exposed to the fluid pressures at both the upstream and the downstream ends of the shunt flow path 20 (i.e. both the pressure at the inlet port 11 and the pressure at the control valve 5). When the difference in pressure across the plunger 63 is sufficient to overcome the biasing force of the spring 64, the plunger will unseat from the cap 62 and oil will be allowed to flow into the shunt flow path 20 through windows 65 provided in the cylindrical sleeve 61.

Allowing for oil flow through the shunt flow path 20 can be advantageous under certain conditions. It is possible for either or both of the heat exchangers 3, 4 to develop clogs along the oil flow path, which can substantially increase the pressure required to force oil through the heat exchanger. Such an increase in head pressure can be damaging to the oil pump, or to the heat exchangers themselves, or to other equipment along the oil circuit. Component damage or failure can be prevented by selecting the biasing force of the spring 63 to be sufficiently low to enable opening the shunt flow path 20 to oil flow prior to reaching such a non-desirable pressure. Furthermore, by integrating the pressure relief valve 6 within the thermal management unit 1 itself, the system can be protected against clogging of both the transmission oil heater 3 and the transmission oil cooler 4. The pressure relief valve 6 is hydraulically in parallel with both of the heat exchangers, so that some amount of the oil can be diverted through the shunt flow path 20 to maintain the pressure head below a threshold limit while allowing the remaining oil to flow through either (or both) of the heat exchangers 3 and 4, depending on the operational state of the control valve 5.

Additional benefits can be derived from the pressure relief valve 6 during startup of the vehicle powertrain 2 under cold ambient temperature conditions. Typical transmission oils are specifically formulated to have a proper viscosity at the expected operating temperature in order to optimize the performance of the vehicle powertrain. These operating temperatures typically are in the range of 80-120 degrees Celsius. As the temperature of the oil decreases, the viscosity tends to increase, and at very cold temperatures (as can be experienced in colder climates) the viscosity tends to increase dramatically. Operating the vehicle powertrain when the transmission oil is at such a low temperature can be problematic in that the high oil viscosity places considerable strain on the oil pump, and can contribute to substantial decreases in fuel economy due to the extra pump work that is required to move the transmission oil through the system. It is nonetheless desirable for the vehicle powertrain to receive a high flow rate of transmission oil.

This high flow rate of highly viscous cold oil can result in substantially high pressure through the system, particularly in the transmission oil heater 3, as the pump works to overcome the viscous resistance to flow. This elevated pressure can again lead to damage in the oil system, or to an undesirable reduction in oil flow. The inclusion of the pressure relief valve 6 mitigates against this issue by allowing for some oil flow through the shunt flow path 20, that oil thereby bypassing the oil heater 3 and reducing the pressure spikes while still allowing for full oil flow through the transmission. The bypassed flow mixes in the control valve 5 with the heated flow being received from the oil heater 3, so that the sensing element is exposed to essentially the mixed temperature of the oil. This prevents against the premature opening of the control valve 5 that would result from an external bypass, wherein only the temperature of the heated oil would be measured by the control valve. Such a premature opening would increase the time required for heating of the oil to the desired operating temperature, thereby decreasing fuel economy.

Various alternatives to the certain features and elements of the present invention are described with reference to specific embodiments of the present invention. With the exception of features, elements, and manners of operation that are mutually exclusive of or are inconsistent with each embodiment described above, it should be noted that the alternative features, elements, and manners of operation described with reference to one particular embodiment are applicable to the other embodiments.

The embodiments described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present invention. As such, it will be appreciated by one having ordinary skill in the art that various changes in the elements and their configuration and arrangement are possible without departing from the spirit and scope of the present invention. 

What is claimed is:
 1. A method of controlling the temperature of oil for a vehicle powertrain, comprising: receiving a flow of oil from the vehicle powertrain into a thermal management unit at a first pressure; directing at least some of the flow of oil through at least one of a transmission oil heater and a transmission oil cooler; receiving said at least some of the flow of oil into a control valve arranged within the thermal management unit after passing through the at least one of a transmission oil heater and a transmission oil cooler, wherein said oil is received into the control valve at a second pressure lower than the first pressure; directing any remaining flow of oil through a bypass arranged within the thermal management unit to avoid passing that remaining flow of oil through either of the transmission oil heater and the transmission oil cooler; measuring a temperature of oil received into the control valve; and returning the flow of oil to the vehicle powertrain from the thermal management unit.
 2. The method of claim 1, wherein the step of directing any remaining flow of oil through the bypass includes flowing said oil through the control valve.
 3. The method of claim 1, wherein the amount of oil passing through the bypass is determined in response to a pressure differential between the first pressure and the second pressure.
 4. The method of claim 1, wherein the step of measuring a temperature of oil includes directing the entire flow of oil received into the thermal management unit over a temperature-responsive element arranged within the control valve.
 5. The method of claim 1, wherein said oil flowing through at least one of a transmission oil heater and a transmission oil cooler is recombined with said oil directed through the bypass prior to exiting the control valve.
 6. A method of managing oil for a vehicle powertrain, comprising: receiving a flow of oil from the vehicle powertrain into a thermal management unit at a first temperature below a threshold temperature; dividing the flow of oil into a first portion and a second portion; directing the first portion into a transmission oil heater integrated into the thermal management unit; heating the first portion in the transmission oil heater; recombining the first portion with the second portion, the second portion having bypassed the transmission oil heater, wherein the recombined flow is at a second temperature higher than the first temperature; receiving the recombined flow of oil into a control valve located within the thermal management unit; passing the recombined flow of oil over a temperature-responsive element arranged within the control valve; and returning the recombined flow of oil to the vehicle powertrain from the thermal management unit at the second temperature.
 7. The method of claim 6, wherein the flow of oil is a first flow of oil, further comprising: receiving a second flow of oil from the vehicle powertrain into the thermal management unit some time after having returned the first flow of oil to the vehicle powertrain; directing substantially all of the second flow of oil into the transmission oil heater; heating the second flow of oil in the transmission oil heater; receiving the second flow of oil into the valve at a temperature substantially equal to the threshold temperature; actuating an actuator of the valve in response to passing the second flow of oil over the temperature-responsive element so that subsequent flows of oil into the thermal management unit are at least partially directed through an oil cooler associated with the vehicle powertrain. 